Optical information recording medium and optical information recording/reproducing apparatus

ABSTRACT

An optical information recording medium, in which a first dielectric layer ( 2 ), a recording layer ( 3 ), a second dielectric layer ( 4 ), and a reflective layer ( 5 ) are sequentially formed in this order on a transparent resin substrate ( 1 ). The recording layer ( 3 ) comprises fine crystal grains ( 7 ) dispersed in a matrix ( 6 ) composed of a dielectric such as SiO 2 . The recording layer ( 3 ) has a thickness of 7 to 15 nm, and the fine crystal grains ( 7 ) have a particle diameter of 3 to 7 nm. The fine crystal grains ( 7 ) are made of an Ag—Pd—Cu alloy composed of 0.3 to 25 mass % of Pd and 0.3 to 25 mass % of Cu, the balance being Ag and unavoidable impurities. Information is recorded or reproduced by irradiating a blue-violet semiconductor laser having a wavelength of 380 to 430 nm to this optical information recording medium.

TECHNICAL FIELD

The present invention relates to an optical information recording mediumon which information is recorded and from which information isreproduced by irradiating a laser beam, and an optical informationrecording/reproducing apparatus for recording and reproducinginformation to and from this optical information recording medium.

BACKGROUND ART

With the rapid propagation of CD-ROM (Compact Disk Read Only Memory) andDVD-ROM (Digital Versatile Disc—ROM), “write once” optical informationrecording media (hereinafter referred to as “optical recording media”,or simply “media”) such as CD-R (Compact Disc Recordable) and DVD-R(Digital Versatile Disc Recordable), on which users can write data onlyonce, have recently been increasingly widespread. In the above mentionedCD-R and DVD-R, a photosensitive dye layer is formed as a recordinglayer on a substrate by a spin coating or deposition method. To achievea reflectance equal to that of CD-ROM and the like, a reflective layermade of metal such as Al or Au is formed on the dye layer. Thesemiconductor laser beam used for the recording and reproduction ofinformation has a wavelength of about 780 nm for CD-R, and about 650 nmfor DVD-R. The dye material being used is selected so that lightabsorption is high enough for the recording with the semiconductor laserbeam having these wavelengths.

Meanwhile, research and development of blue-violet semiconductor laserhas recently progressed rapidly, and semiconductor laser with awavelength of 380 to 430 nm will soon begin to be used. The recordingdensity of optical recording media primarily depends on the focus spotsize of light beam used for the recording and reproduction ofinformation. As the focus spot size is proportional to the wavelength oflight beam, it will become smaller if a blue-violet semiconductor laserbeam with a shorter wavelength is used rather than the red semiconductorlaser that is currently being used, whereby the recording capacity ofoptical recording media is expected to increase largely.

Apart from the method that uses the above described photosensitive dyelayer, there has been proposed another optical recording medium thatuses such a blue-violet semiconductor laser beam, wherein the recordinglayer is a super-thin insular metal film that is formed of finedispersed particles of metal such as Au, Ag, or Cu, the thin film beingformed on a spacer layer made of transparent organic resin. Thesuper-thin insular metal film can be obtained by a deposition or asputtering method in which the metal film deposition is stopped at aninitial stage. With this optical recording medium, marks are formed bybubble-forming of transparent resin or mutual diffusion of two types ofmetal, triggered by laser irradiation (see, for example, Patent Document1: Japanese Patent Laid-Open No. 2002-11957, and Non-Patent Document 1:Extended Abstracts, The 50th Meeting of Japan Society of Applied Physicsand Related Societies, 27p-ZW-4).

In another optical recording medium that has been proposed so far, athin film of metal, semiconductor, or the like is formed as a recordinglayer on a PC (polycarbonate) substrate, and laser is irradiated to heatthis thin film and to cause deformation of the thin film and thesubstrate in the heated portion, so that information is recorded.

[Patent Document 1]: Japanese Patent Laid-Open Publication No.2002-11957

[Non-Patent Document 1]: Extended Abstracts, The 50th Meeting of JapanSociety of Applied Physics and Related Societies, 27p-ZW-4.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The above described conventional techniques, however, had the followingdrawbacks: First, as for the optical recording medium that uses a dyelayer as the recording layer, the dye material suitable for ablue-violet semiconductor laser beam having a wavelength of 380 to 430nm is still being developed and a material that can actually be used isyet to be developed. More specifically, after information is recorded byforming a mark in the dye layer, when a reproducing laser beam isirradiated to this mark for a certain length of time, the recordedinformation will eventually be deteriorated. Another drawback is thatthe production process of the optical recording medium with a dye layeris complex because it requires another sputtering process step or thelike to form a reflective layer after the dye material has been coatedon the substrate by spin coating. A further drawback is that in a mediumwith a dye recording layer, light transmission of the recording layer islow, and such a structure is not suitable for the production of opticalinformation recording medium having two or more recording layers formultilayer recording.

In an optical recording medium wherein the recording layer is asuper-thin insular metal film made of fine dispersed particles of metalsuch as Au, Ag, or Cu and this insular metal film is interposed betweenorganic resin films, the recording layer has a dispersed particlestructure in which metal particles with a diameter ranging from a fewnanometers to several tens nanometers are distributed two-dimensionally.The amount of metal particles is therefore very small, and when the diskis rotated at high speed during information recording, the recordinglaser power becomes insufficient, because of which a recording mark witha high signal quality is hard to form. Also, because of the dispersedparticle structure with two-dimensionally distributed metal particles,noise is high during reproduction. Further, the film thickness of theinsular metal film is hard to control because it must be limited to avery small range of about 10 nm or lower. Furthermore, because theorganic resin films are formed by spin coating, the production processis complex.

As for the optical recording medium on which information is recorded bydeformation of the thin film and substrate triggered by laserirradiation, a noise increase is distinct because of the substratedeformation during recording, and a low-noise reproducing signal is hardto achieve. When the groove pitch is reduced for higher density, inparticular, or in land/groove recording wherein information is recordedon both of the grooves of the substrate and flat lands between thegrooves, the influence of substrate deformation during recording extendsto adjacent recording areas, and high density recording is hard toachieve.

The present invention was devised in view of these problems, and anobject of the invention is to provide an optical information recordingmedium which is easily producible and achieves high quality ofreproducing signal even with the use of a blue-violet semiconductorlaser beam for the recording and reproduction and which is capable ofmultilayer recording, and an optical information recording/reproducingapparatus for recording information on this optical informationrecording medium and for reproducing the information.

MEANS FOR SOLVING THE PROBLEMS

An optical information recording medium according to the presentinvention includes a substrate and a recording layer formed on thesubstrate, information being recorded and reproduced by irradiatinglight to this recording layer, and is characterized in that therecording layer includes a matrix made of a dielectric and a pluralityof fine crystal grains made of a metal or an alloy and dispersed in thematrix, and, by irradiating light to the recording layer, a size of thefine crystal grains is changed in a portion irradiated by the light,whereby information is recorded.

According to the invention, by irradiating light to the recording layer,the size of the fine crystal grains is changed in the irradiated portionof the recording layer, and the reflectance in this irradiated portionchanges. Thereby, a mark is formed in the irradiated portion of therecording layer, and information is recorded. This optical informationrecording medium is easily producible because there is no need offorming an organic resin film by means of spin coating or the like.

Preferably, the fine crystal grains should be made of a metal or analloy of two or more metals selected from the group consisting of Ag,Cu, In, Pd, and Te. The fine crystal grains should preferably be made ofan Ag—Pd—Cu alloy containing 0.3 to 25 mass % of Pd and 0.3 to 25 mass %of Cu, the balance being Ag and unavoidable impurities, or an Ag—Tealloy containing 38 to 55 mass % of Te, the balance being Ag andunavoidable impurities, or a Cu—In alloy containing 40 to 95 mass % ofIn, the balance being Cu and unavoidable impurities. Thereby, goodrecording/reproducing characteristics and good corrosion resistance areboth achieved.

Furthermore, the recording layer may consist of a plurality of layers,which are separated from each other by an interlayer optical separationlayer. Thereby, information is recorded in each of the plurality oflayers, and the recording density of the optical information recordingmedium is increased.

Further, the light should preferably be a laser beam with a wavelengthof 380 to 430 nm. Thereby, a small spot can be formed on the recordinglayer and the recording density can be increased.

An optical information recording/reproducing apparatus according to thepresent invention is characterized in that light is irradiated to theabove described optical information recording medium to change the sizeof the fine crystal grains in a portion of the recording layerirradiated by the light and to change the reflectance of this portion sothat information is recorded, and the information is reproduced bydetecting a difference in the reflectance of the recording layer.

ADVANTAGE OF THE INVENTION

According to this invention, the size of the fine crystal grains of therecording layer is changed by irradiating light so that information isrecorded. Thus an optical information recording medium that is easilyproducible and achieves high quality of reproducing signal even with theuse of a blue-violet semiconductor laser beam for the recording andreproduction is realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a first embodiment of theoptical information recording medium of the invention;

FIG. 2 is a cross-sectional view illustrating a second embodiment of theoptical information recording medium of the invention;

FIG. 3 is a cross-sectional view illustrating a third embodiment of theoptical information recording medium of the invention;

FIG. 4 is a block diagram illustrating a fifth embodiment of the opticalinformation recording/reproducing apparatus of the invention; and

FIG. 5 is a graph showing the influence of linear speed on the qualityof reproduction signal, the horizontal axis representing the linearspeed of the optical disk medium during recording and reproduction andthe vertical axis representing the C/N ratio of 8T signal.

DESCRIPTION OF REFERENCE NUMERALS

-   1 Transparent resin substrate;-   2, 2 a First dielectric layer;-   2 b Third dielectric layer;-   3 Recording layer;-   3 a First recording layer;-   3 b Second recording layer;-   4, 4 a Second dielectric layer;-   4 b Fourth dielectric layer;-   5 Reflective layer;-   6 Matrix;-   7 Fine crystal grains;-   8 Optical separation layer;-   9 Dummy transparent resin substrate;-   100 Disk;-   101 Spindle motor;-   102 Rotation control circuit;-   103 Servo control circuit;-   104 Optical head;-   105 Recording/reproducing circuit;-   106 Wobble detection circuit;-   107 Address detection circuit;-   108 Recorded data processing circuit;-   109 Synchronizing signal generation circuit;-   110 Reproduced data processing circuit;-   111 Interface;-   112 Controller

BEST MODE FOR CARRYING OUT THE INVENTION

Specific embodiments of the present invention will be hereinafterdescribed with reference to the accompanying drawings. A firstembodiment of the invention will be described first. FIG. 1 is across-sectional view illustrating the optical information recordingmedium according to the present embodiment. In this specification, thescale in vertical and horizontal directions and the aspect ratio of thedrawings are discretionary.

As shown in FIG. 1, the optical recording medium according to thepresent embodiment includes a disk-like transparent resin substrate 1.The transparent resin substrate 1 has a diameter of, for example, 120mm, and a thickness of, for example, 0.6 mm, and is formed with guidegrooves or pre-pits (not shown) on the surface. A first dielectric layer2, a recording layer 3, a second dielectric layer 4, and a reflectivelayer 5 are sequentially formed in this order on the transparent resinsubstrate 1. On the reflective layer 5 is formed a UV curable resinlayer (not shown), on which a 0.6 mm thick dummy transparent resinsubstrate is bonded (not shown). The transparent resin substrate 1 andthe dummy transparent resin substrate are, for example, PC substrates.The first dielectric layer 2 and the second dielectric layer 4 are madeof, for example, ZnS—SiO₂. The reflective layer 5 is made of, forexample, an AlTi alloy.

The recording layer 3 contains fine crystal grains 7 of metal or alloydispersed in a dielectric matrix 6. The dielectric forming the matrix 6is, for example, an oxide dielectric, such as silicon oxide (SiO₂). Thefine crystal grains 7 are made of a metal or an alloy of two or moremetals selected from the group consisting of, for example, silver (Ag),copper (Cu), indium (In), palladium (Pd), and tellurium (Te); it is, forexample, an Ag—Pd—Cu alloy containing 0.3 to 25 mass % of Pd and 0.3 to25 mass % of Cu, the balance being Ag and unavoidable impurities. Therecording layer 3 has a thickness of, for example, 5 to 25 nm, morespecifically 7 to 15 nm, and is a polycrystalline layer. The recordinglayer 3 contains fine crystal grains 7 at a rate of, for example, 30 to80 volume %. The fine crystal grains 7 should preferably have a particlediameter of not more than 10 nm, and more specifically 3 to 7 nm.

The dielectric forming the matrix 6 is not limited to silicon oxide(SiO₂) and may be, for example, aluminum oxide (Al₂O₃) or tantalum oxide(Ta₂O₅). Alternatively, the dielectric forming the matrix 6 may be anitride dielectric, such as silicon nitride (SiN), aluminum nitride(AlN), or tantalum nitride (TaN). Or it may be a mixture or a compoundof two or more of the above listed oxides and/or nitrides.

The metal or alloy forming the fine crystal grains 7 is not limited tothe Ag—Pd—Cu alloy, and may be, for example, an Ag—Te alloy containing38 to 55 mass % of Te, the balance being Ag and unavoidable impurities,or a Cu—In alloy containing 40 to 95 mass % of In, the balance being Cuand unavoidable impurities. In these cases, too, the content andparticle diameter of the fine crystal grains 7 should preferably bewithin the above noted ranges.

The followings are the reasons for the numerical limitations on variousconstituent elements of the present invention.

Thickness of Recording Layer: 5 to 25 nm

If the thickness of the recording layer is less than 5 nm, the lighttransmission will be high and light absorption will be low in therecording layer, which makes it hard to record information. On the otherhand, if the thickness of the recording layer exceeds 25 nm, then thereflectance of the recording layer will be too high, which will lowerthe light absorption, making it hard to record information. Therefore,the recording layer should preferably have a thickness of 5 to 25 nm.More preferably, it may be 7 to 15 nm.

Contents of Pd and Cu when the Fine Crystal Grains are Made of anAg—Pd—Cu Alloy: 0.3 to 25 mass %

Ag itself has low corrosion resistance to sulfur and chloridecomponents. Pd on the other hand is stable relative to sulfur andchloride. Therefore, adding Pd to Ag in a range of 0.1 to 30.0 mass %increases the corrosion resistance. Note, an alloy consisting only of Agand Pd has low corrosion resistance in a high temperature, high moistureatmosphere, and an Ag—Pd alloy medium may corrode if it is left in suchan environment. However, adding Cu to the Ag—Pd alloy in a range of 0.1to 30.0 mass % increases the corrosion resistance in a high temperature,high moisture atmosphere. In the above noted ranges of composition, ifPb content is 0.3 to 25 mass % and Cu content is 0.3 to 25 mass %, therecording/reproducing characteristics are particularly favorable.Therefore, the contents of Pd and Cu in the Ag—Pd—Cu alloy shouldpreferably be 0.3 to 25 mass %, respectively.

Content of Te when the Fine Crystal Grains are Made of an Ag—Te Alloy:38 to 55 mass %

As mentioned above, while Ag itself has low corrosion resistance tosulfur and chloride contents, if Te is added in an amount of 33 mass %or more, its corrosion resistance to sulfur and chloride contents isimproved. Meanwhile, as the Te content in the Ag—Te alloy is increased,the melting point of the Ag—Te alloy is lowered. If the melting point ofthe Ag—Te alloy is too high, a high laser power is required to recordinformation, and if the melting point of the Ag—Te alloy is too low, thestorage stability of recorded information may be deteriorated. If anAg—Te alloy is to be used for forming the above noted fine crystalgrains of the recording layer, the melting point of the Ag—Te alloyshould preferably be in a range of 400 to 700° C. The correspondingrange of the mixture rate of Te is 38 to 55 mass %. Therefore, the Tecontent in the Ag—Te alloy should preferably be in a range of 38 to 55mass %.

Content of In when the Fine Crystal Grains are Made of an Cu—In Alloy:40 to 95 mass % Cu itself has a melting point of about 1083° C., and ifthe fine crystal grains are made of Cu alone, then an extremely highlaser power is necessary to record information by laser irradiation.Therefore, it is preferable to add In having a lower melting point to Cuand to form the fine crystal grains from a Cu—In alloy that has a lowermelting point than Cu alone. As mentioned above, the material formingthe fine crystal grains should preferably have a melting point of about400 to 700° C.; adding In in an amount of 40 to 95 mass % makes themelting point of the Cu—In alloy to be in this temperature range. Thereproducing characteristics are also favorable, when the fine crystalgrains are made of a Cu—In alloy with this range of composition.Therefore, the In content in the Cu—In alloy should preferably be in arange of 40 to 95 mass %.

Next, the method of producing this embodiment of the optical recordingmedium will be described. Using an inline sputtering machine, each ofthe layers described below is formed sequentially on the transparentresin substrate 1, on which laser-guiding grooves or pre-pits (notshown) have been formed beforehand. A ZnS—SiO₂ film is first depositedby sputtering to form the first dielectric layer 2. Next, co-sputteringis performed using two targets at the same time, one being SiO₂ and theother being Al—Cu—Pd alloy, for example. This forms the recording layer3, consisting of a matrix 6 of SiO₂ and fine crystal grains 7 ofAl—Cu—Pd alloy dispersed in the matrix. Next, a ZnS—SiO₂ film isdeposited by sputtering to form the second dielectric layer 4. Next, anAl—Ti alloy film is deposited by sputtering to form the reflective layer5. Then, the dummy transparent resin substrate is stacked on thereflective layer 5 via a UV curable resin layer, and UV light isirradiated to cure the UV curable resin layer to bond the dummytransparent resin substrate on the reflective layer 5. The opticalrecording medium according to the present embodiment is thus produced.

Next, a description will be given on the operation of the opticalrecording medium according to the present embodiment structured asdescribed above. When recording information on this optical recordingmedium, a blue-violet semiconductor laser beam having a wavelength of,for example, 380 to 430 nm is made incident from the side of thetransparent resin substrate 1, as a recording laser beam. The recordinglaser beam is passed through the transparent resin substrate 1 and thefirst dielectric layer 2, and irradiated to the recording layer 3. Thelaser beam that has passed through the recording layer 3 further passesthrough the second dielectric layer 4, is reflected by the reflectivelayer 5, passes through the second dielectric layer 4 again, and isirradiated to the recording layer 3. This heats up the laser-irradiatedportion of the recording layer 3, melting the fine crystal grains 7 inthis portion and making adjacent fine crystal grains 7 to cohere, as aresult of which the particle diameter of the fine crystal grains 7becomes larger than that before the laser irradiation. With the changein the particle diameter, the optical constants of the laser-irradiatedportion of the recording layer 3, such as the index of refraction andextinction coefficient, change, and the reflectance is lowered. Forexample, the reflectance of the recording layer 3, which is 20% beforethe laser irradiation, reduces to 7% by the laser irradiation. Thus, thelaser-irradiated portion of the recording layer 3 is formed with a markhaving lower light reflectance than the surroundings, wherebyinformation is recorded.

When reproducing the recorded information, a reproducing laser beamhaving a lower intensity than the above mentioned recording laser beamis made incident from the side of the transparent resin substrate 1. Thereproducing laser beam may have, for example, the same wavelength asthat of the recording laser beam. The reproducing laser beam passesthrough the transparent resin substrate 1 and the first dielectric layer2, is irradiated to the recording layer 3, reflected by the recordinglayer 3, passes through the first dielectric layer 2 and the transparentresin substrate 1 again, and is output to the outside of the opticalrecording medium. The laser beam that has passed through the recordinglayer 3 passes through the second dielectric layer 4, is reflected bythe reflective layer 5, passes through the second dielectric layer 4,the recording layer 3, the first dielectric layer 2, and the transparentresin substrate 1 again, and is output to the outside. Since the lightreflectance is different in the mark (recorded portion) from that inother parts (non-recorded portions) in the recording layer 3, there is adifference in the amount of feedback light (reflected light amount)between the mark and other parts. By detecting the difference in thelight amount, information recorded in the recording layer 3 can be readout.

According to the present embodiment, as described above, sinceinformation is recorded by changing the particle diameter of the finecrystal grains through fusion and cohesion triggered by laserirradiation, the quality of reproducing signal is high even with the useof a blue-violet semiconductor laser beam. Also, because the recordinglayer does not contain a dye, the mark (recorded portion) does notdeteriorate. Further, since there is no deformation of the PC substratein the laser-irradiated portion at the time of recording, there is noincrease in noise at the time of reproduction. Furthermore, while, inthe optical recording medium described in the above mentioned PatentDocument 1 and Non-Patent Document 1, marks are formed by creating adisturbance in particle distribution by bubble-forming of thetransparent resin layer, in the present embodiment, marks are formed bychanging the size and shape of the fine crystal grains through fusionand cohesion. Therefore, as compared to the techniques described in theabove mentioned Patent Document 1 and Non-Patent Document 1, thedifference in the reflectance between the mark portion and non-markportion is large, and the quality of the reproducing signal is high inthe present embodiment. Accordingly, the optical recording mediumaccording to the present embodiment is also suitable for high densityrecording/reproduction such as land/groove recording.

Furthermore, since the layers can be sequentially formed using only asputtering method from the first dielectric layer 2 to the reflectivelayer 5 and there is no need to form a resin layer in the middle step bya spin coating method or the like, the manufacturing process is simpleand production is easy. Also, since there is no need to deposit asuper-thin layer, the production conditions are readily controlled.Moreover, since the recording layer is formed by co-sputtering using analloy target and a dielectric target, a polycrystalline film is formedin which fine crystal grains are uniformly dispersed in the matrix. As aresult, an optical recording medium, for which a blue-violetsemiconductor laser beam can be used, which achieves high quality ofreproducing signal, and which is readily producible, is realized.

Next, a second embodiment of the present invention is described. FIG. 2is a cross-sectional view illustrating the optical information recordingmedium according to the present embodiment. As shown in FIG. 2, theoptical recording medium according to the present embodiment includes adisk-like transparent resin substrate 1, which has a diameter of, forexample, 120 mm, and a thickness of, for example, 1.2 mm. A reflectivelayer 5, a first dielectric layer 2, a recording layer 3, and a seconddielectric layer 4, are sequentially formed in this order from thesubstrate side on the transparent resin substrate 1. On the seconddielectric layer 4 is formed a UV curable resin layer (not shown), onwhich a 100 μm thick transparent PC film is bonded (not shown) to form aPC cover layer. The recording layer 3 contains fine crystal grains 7 ofmetal or alloy dispersed in a dielectric matrix 6. The dielectricforming the matrix 6 is, for example, an oxide dielectric, such assilicon oxide (SiO₂). The fine crystal grains 7 are made of a metal oran alloy of two or more metals selected from the group consisting of,for example, silver (Ag), copper (Cu), indium (In), palladium (Pd), andtellurium (Te); it is, for example, an Ag—Pd—Cu alloy containing 0.3 to25 mass % of Pd and 0.3 to 25 mass % of Cu, the balance being Ag andunavoidable impurities. The features of this embodiment other than thosedescribed above are the same as those of the first embodiment describedin the foregoing.

Next, the method of producing the optical recording medium according tothe present embodiment will be described. An Al—Ti alloy film isdeposited, for example, by a sputtering method on the transparent resinsubstrate 1 to form the reflective layer 5. Next, a ZnS—SiO₂ film isdeposited by a sputtering method to form the first dielectric layer 2.Then, again by a sputtering method, co-sputtering is performed using twotargets at the same time, one being SiO₂ and the other being Al—Cu—Pdalloy, for example. This forms the recording layer 3, comprising amatrix 6 of SiO₂ and fine crystal grains 7 of Al—Cu—Pd alloy dispersedin the matrix. Next, a ZnS—SiO₂ film is deposited by a sputtering methodto form the second dielectric layer 4. Then, through a UV curable resinlayer, the transparent PC film is bonded on the second dielectric layer4 as a light transmission layer to form the PC cover layer. The opticalrecording medium according to the present embodiment is thus produced.With the optical recording medium according to the present embodiment,the recording laser beam and the reproducing laser beam are madeincident from the side of the PC film. The operation and effects of thepresent embodiment are the same as those of the first embodimentdescribed in the foregoing.

Next, a third embodiment of the present invention is described. FIG. 3is a cross-sectional view illustrating the optical information recordingmedium according to the present embodiment. As shown in FIG. 3, theoptical recording medium according to the present embodiment includes adouble-layer recording layer. That is, the medium includes a disk-liketransparent resin substrate 1, which has a diameter of, for example, 120mm, and a thickness of, for example, 0.6 mm, and on this transparentresin substrate 1, a first dielectric layer 2 a, a first recording layer3 a, a second dielectric layer 4 a, an optical separation layer 8, athird dielectric layer 2 b, a second recording layer 3 b, a fourthdielectric layer 4 b, a reflective layer 5, a UV curable resin layer(not shown), and a dummy transparent resin substrate 9 are sequentiallyformed in this order from the side of the substrate 1. The firstrecording layer 3 a has a thickness of, for example, 7 nm, and thesecond recording layer 3 b has a thickness of, for example, 12 nm. Thefirst and second recording layers 3 a and 3 b contain fine crystalgrains 7 dispersed in a matrix 6. The optical separation layer 8 ismade, for example, of a UV curable resin. With the optical recordingmedium according to the present embodiment, the recording laser beam andthe reproducing laser beam are made incident from the side of thetransparent resin substrate 1. The features other than those describedabove, production method and operation of the present embodiment are thesame as those of the first embodiment described in the foregoing.

In the present embodiment, since the recording layer does not containany dye material, the recording layer has high light transmission, andcan have the double-layer structure. Thereby, the recording density canbe made twice higher than that of an optical recording medium having asingle-layer recording layer. The effects of the present embodimentother than the above are the same as those of the first embodimentdescribed in the foregoing.

Next, a fourth embodiment of the present invention is described. Theoptical recording medium according to the present embodiment includes atransparent resin substrate having a thickness of, for example, 1.2 mm,and a reflective layer, a dielectric layer, a second recording layer, adielectric layer, an optical separation layer, a dielectric layer, afirst recording layer, a dielectric layer, a UV curable resin layer, anda PC cover layer are sequentially formed in this order on thetransparent resin substrate. With this optical recording medium, therecording laser beam and the reproducing laser beam are made incidentfrom the side of the PC cover layer. The features other than thosedescribed above, operation and effects of the present embodiment are thesame as those of the third embodiment described in the foregoing.

While the recording layer of the third and fourth embodiments describedabove has a double-layer structure, it may have three or more layers.Thereby, the recording density can further be increased.

Next, a fifth embodiment of the present invention is described. This isone embodiment of an optical information recording/reproducing apparatus(hereinafter also referred to simply as “recording/reproducingapparatus”) for recording and reproducing information to and from theoptical recording media according to the first to fourth embodimentsdescribed above. FIG. 4 is a block diagram illustrating the opticalinformation recording/reproducing apparatus according to the presentembodiment. As shown in FIG. 4, the recording/reproducing apparatusaccording to the present embodiment includes a spindle motor 101 forsupporting and rotating a disk 100, which is the optical recordingmedium, and a rotation control circuit 102 for controlling the rotationof this spindle motor 101. The disk 100 is one of the optical recordingmedia according to the first to fourth embodiments.

This recording/reproducing apparatus also includes an optical head 104,which includes a laser source (not shown) for irradiating a blue-violetsemiconductor laser beam having a wavelength of, for example, 380 to 430nm to the disk 100 as the recording laser beam and the reproducing laserbeam, and a photodetector (not shown) for detecting feedback light fromthe disk 100. The apparatus further includes a servo control circuit 103for controlling the position, focusing, and tracking of the optical head104.

The apparatus further includes a recording/reproducing circuit 105,which, when recording, drives the laser source inside the optical head104 to focus the recording laser beam to a predetermined position on therotating optical disk 100 to record information, and which, whenreproducing, causes the laser source inside the optical head 104 tooutput the reproducing laser beam and causes the photodetector insidethe optical head 104 to detect feedback light from the disk 100, toreproduce the recorded information based on the detection results. Therecording/reproducing circuit 105 generates a reproduced data signal inaccordance with the information recorded on the disk 100, as well asother signals such as a wobble signal indicative of the irradiatedposition on the disk, a focus servo error signal indicating a focuserror, a tracking servo error signal indicating a tracking error, andthe like, based on the output signal from the photodetector.

The apparatus further includes a wobble detection circuit 106 fordetecting a wobble signal from the signal output from therecording/reproducing circuit 105, and an address detection circuit 107that detects address information indicating the focus position of thelaser beam on the optical disk 100 by demodulating and decoding theoutput signal from the wobble detection circuit 106. The apparatusfurther includes a synchronizing signal generation circuit 109 forgenerating a synchronizing signal in accordance with the output signalfrom the wobble detection circuit 106, and a reproduced data processingcircuit 110 that demodulates the reproduced data signal output from therecording/reproducing circuit 105 based on the synchronizing signal fromthe synchronizing signal generation circuit 109 and corrects the errorin the reproduced data signal to generate reproduced data.

Furthermore, an interface 111 is provided, which performs the followingfunctions: Output reproduced data that is input from the reproduced dataprocessing circuit 110 to an outside host computer (not shown); outputrecorded data that is input from the host computer to a recorded dataprocessing circuit 108; and output recording/reproducing instructiondata that is input from the host computer to a controller 112 that willbe described later.

Furthermore, a recorded data processing circuit 108 is provided, whichreceives recorded data from the interface 111, adds an error correctioncode to the recorded data, converts data into a format suitable for therecording, and modulates and outputs the data to therecording/reproducing circuit 105. Furthermore, a controller 112 isprovided, to which the recording/reproducing instruction data is inputfrom the interface 111, address information is input from the addressdetection circuit 107, and a feedback signal is input from the servocontrol circuit 103, and which controls the rotation control circuit102, the servo control circuit 103, and the recording/reproducingcircuit 105.

Next, a description will be given with reference to FIG. 4 on theoperation of the recording/reproducing apparatus according to thepresent embodiment structured as described above. First, the operationwhen information is recorded on the disk 100 will be described.Recording instruction data and data to be recorded are first input fromthe host computer to the interface 111. The interface 111 outputs therecording instruction data to the controller 112, and outputs the datato be recorded to the recorded data processing circuit 108. Thecontroller 112 outputs a control signal to the rotation control circuit102, which in turn drives the spindle motor 101 to rotate the disk 100.

Meanwhile, the recorded data processing circuit 108 adds an errorcorrection code to the data to be recorded input from the interface 111,converts data into a format suitable for the recording, modulates thedata, and outputs the data to the recording/reproducing circuit 105. Therecording/reproducing circuit 105 drives the laser source inside theoptical head 104 in accordance with the data to be recorded, to focusthe recording laser beam from the laser source to a predeterminedposition on the rotating optical disk 100. The recording laser beam is ablue-violet semiconductor laser beam having a wavelength of, forexample, 380 to 430 nm. Thereby, marks are formed in the recording layerof the optical disk 100 by the principle described in the section of thefirst embodiment above, and thus information is recorded.

At the same time, the photodetector in the optical head 104 outputs adetection signal to the recording/reproducing circuit 105, which, basedon this signal, generates a wobble signal, a focus servo error signal,and a tracking servo error signal, and outputs these signals to thewobble detection circuit 106. The wobble detection circuit 106 detectsthe wobble signal from the signal output from the recording/reproducingcircuit 105, outputs the wobble signal together with the focus servoerror signal and the tracking servo error signal to the addressdetection circuit 107, and outputs the wobble signal to thesynchronizing signal generation circuit 109.

The address detection circuit 107 demodulates and decodes the signaloutput from the wobble detection circuit 106 so as to detect addressinformation indicative of the focus position of the light beam on theoptical disk 100, and outputs the information to the controller 112 withthe focus servo error signal and tracking servo error signal. Thecontroller 112 controls the servo control circuit 103 based on theaddress information, the focus servo error signal, and the trackingservo error signal, and the servo control circuit 103 controls theposition, focusing, and tracking of the optical head 104. At the sametime, the servo control circuit 103 outputs a feedback signal to thecontroller 112. The synchronizing signal generation circuit 109generates and outputs a synchronizing signal to the recorded dataprocessing circuit 108.

Next, the operation when the information recorded on the disk 100 isreproduced will be described. First, the host computer inputs areproduction instruction data to the interface 111. The interface 111outputs this reproduction instruction data to the controller 112. Thecontroller 112 outputs a control signal to the rotation control circuit102, which in turn drives the spindle motor 101 to rotate the disk 100.The controller 112 also outputs a control signal to therecording/reproducing circuit 105, which in turn drives the optical head104 to output a reproducing laser beam from the laser source in theoptical head 104 to the disk 100, and the photodetector in the opticalhead 104 detects feedback light from the disk 100. The reproducing laserbeam is a blue-violet semiconductor laser beam having a wavelength of,for example, 380 to 430 nm. Thereby, information recorded on the disk100 is read out by the principle described in the section of the firstembodiment above.

An output signal from the photodetector of the optical head 104 is inputto the recording/reproducing circuit 105, which, based on this outputsignal, then generates a reproduced data signal, a wobble signal, afocus servo error signal, and a tracking servo error signal, outputs thereproduced data signal to the reproduced data processing circuit 110,and outputs the wobble signal, the focus servo error signal, and thetracking servo error signal to the wobble detection circuit 106. Thewobble detection circuit 106 outputs the wobble signal to thesynchronizing signal generation circuit 109, which, based on the wobblesignal, generates a synchronizing signal and outputs it to thereproduced data processing circuit 110. The reproduced data processingcircuit 110 demodulates the reproduced data signal based on thesynchronizing signal, and corrects errors in the reproduced data signalto generate reproduced data, which is then output to the interface 111.The interface 111 outputs this reproduced data to the outside hostcomputer. Thereby, information recorded on the disk 100 is reproduced.At the same time, the servo control circuit 103 controls the position,focusing, and tracking of the optical head 104 in the same manner as inthe information recording described in the foregoing.

The optical information recording/reproducing apparatus according to thepresent embodiment can record information to any of the opticalrecording media described above according to the first to fourthembodiments, and reproduce this information. This enables the use of ablue-violet semiconductor laser beam as the recording and thereproducing laser beam, whereby the recording density of the opticalrecording medium can be improved.

EXAMPLE 1

Specific examples of the present invention will be described below.First, with the methods described in the sections of the first andsecond embodiments above, optical disk media (optical informationrecording media) to be evaluated were produced. Two types of opticaldisk media were produced, one being an optical disk medium to which alaser beam is made incident from the side of the transparent resinsubstrate as described in the first embodiment above (hereinafterreferred to as “substrate-side incident type medium”), and the otherbeing an optical disk medium to which a laser beam is made incident fromthe side of the cover layer (PC film) as described in the secondembodiment above (hereinafter referred to as “cover layer-side incidenttype medium”). That is, each layer was sequentially formed on atransparent resin substrate pre-formed with guide grooves or pre-pits,using an inline sputtering machine. The layer structure of each mediumis as follows. In the following description, the structure wherein “Alayer,” “B layer,” and “C layer” are formed sequentially from the sideof the substrate will be represented as A/B/C. The layer structure ofthe substrate-side incident type medium was PC substrate/firstdielectric layer/recording layer/second dielectric layer/AlTi reflectivelayer/UV adhesive layer/dummy PC substrate. The layer structure of thecover layer-side incident type medium was PC Substrate/AlTi reflectivelayer/first dielectric layer/recording layer/second dielectric layer/UVadhesive layer/PC cover layer.

The recording layer was deposited by co-sputtering using two sputteringtargets, one being an alloy target of a predetermined composition, andthe other being a dielectric target. The compositions of the matrix andfine crystal grains of the recording layer were different in each of themedia. Power was applied independently for each target, each beingadjusted during the film deposition so that the fine crystal grains ofalloy were uniformly dispersed in the dielectric matrix. The substratewas arranged parallel and opposite each target, and revolved at arotation speed of 40 rpm. The transparent resin substrate passes abovethe alloy target and the dielectric target alternately by this revolvingmotion, whereby the fine crystal grains were made to disperse uniformlyin the recording layer. A ZnS—SiO₂ film was formed as the dielectriclayer, and an AlTi film was formed as the reflective layer 5.

The recording/reproducing characteristics of the optical disk mediumproduced as described above were evaluated. The evaluation included thefollowing: Using the optical information recording/reproducing apparatusof the fifth embodiment (see FIG. 4) described above, a signal with aperiod of 8T was recorded with a recording power with which noise isminimal, and the reproducing signal quality and the reproducing lightresistance of this signal were evaluated. The evaluation of thereproducing signal quality was done by reproducing the above mentioned8T signal and measuring its C/N ratio (carrier to noise ratio). If theC/N ratio is 53 dB or more, it is determined that the reproducing signalhas good quality. The evaluation of the reproducing light resistance wasdone by reproducing the same track 100,000 times with a power largerthan the reproducing power by 0.2 mW (see Table 1) and measuring adifference from the initial value of C/N ratio of 8T signal. Some of theoptical disk media were picked up to observe the recorded portions andnon-recorded portions in the recording layer with a TEM (transmissionelectronic microscope) and to measure the particle diameter of the finecrystal grains. Table 1 shows the measurement conditions. Table 2 showsthe compositions of the fine crystal grains and matrix of the recordinglayer, recording power, reproducing signal quality (C/N ratio of 8Tsignal), and reproducing light resistance (difference in the C/N ratioof 8T signal). In Table 2, “Ag₉₈Pd₁Cu₁”, for example, represents anAg—Pd—Cu alloy having a composition of 98 mass % of Ag, 1 mass % of Pd,and 1 mass % of Cu. This presentation rule also applies to otherexamples in the following. Also, “substrate” in the column “layerstructure” represents the substrate-side incident type medium, and“cover” represents the cover layer-side incident type medium. TABLE 1Substrate-side Cover layer-side incident type incident type Medium typemedium medium Laser beam 405 nm 405 nm wavelength (λ) Numerical aperture0.65 0.85 of lens (NA) Linear speed (m/sec) 5.6 5.1 Recording frequency55 MHz 66 MHz Recording power 6-12 mW 3-7.5 mW Reproducing power 0.5 mW0.4 mW

TABLE 2 Re- Recording layer Re- producing Exam- Fine cording 8T lightple Layer crystal power C/N resistance No. structure grains Matrix (mW)(dB) (dB) 1 Substrate Ag₉₈Pd₁Cu₁ SiO₂ 10.5 56.3 0 2 Substrate Ag₉₈Pd₁Cu₁Al₂O₃ 10.3 55.8 0 3 Substrate Ag₉₈Pd₁Cu₁ Ta₂O₅ 10.8 55.6 0 4 SubstrateAg₉₈Pd₁Cu₁ SiN 10.7 56.2 0 5 Substrate Ag₉₈Pd₁Cu₁ AlN 10.9 55.7 0 6Substrate Ag₉₈Pd₁Cu₁ TaN 10.6 55.9 0 7 Cover Ag₉₈Pd₁Cu₁ SiO₂ 6.3 55.8 08 Cover Ag₉₈Pd₁Cu₁ Al₂O₃ 6.2 55.4 0 9 Cover Ag₉₈Pd₁Cu₁ Ta₂O₅ 6.6 55.6 010 Cover Ag₉₈Pd₁Cu₁ SiN 6.5 55.7 0 11 Cover Ag₉₈Pd₁Cu₁ AlN 6.6 54.8 0 12Cover Ag₉₈Pd₁Cu₁ TaN 6.4 55.2 0

In the optical disk media of No. 1 and No. 7 shown in Table 2, theparticle diameter of the fine crystal grains of the recording layer wasabout 3 to 7 nm in the non-recorded portions, and 30 to 80 nm in therecorded portions. This indicates that laser irradiation has increasedthe particle diameter of the fine crystal grains.

As shown in Table 2, the optical information recording media with arecording layer that is formed by co-sputtering from the fine crystalgrains of Ag₉₈Pd₁Cu₁ (mass %) alloy and the matrix of an oxidedielectric or a nitride dielectric exhibited a high reproducing C/Nratio and good reproducing light resistance.

EXAMPLE 2

Optical disk media having fine crystal grains formed of Ag—Te alloy wereproduced with the same method as Example 1 described above, and theircharacteristics were evaluated. The optical disk media had two layerstructures, one being the substrate-side incident type medium as withthe above described first embodiment and the other being the coverlayer-side incident type medium as with the above described secondembodiment. Table 3 shows the compositions of the fine crystal grainsand matrix of the recording layer, recording power, reproducing signalquality (C/N ratio of 8T signal), and reproducing light resistance(difference in the C/N ratio of 8T signal). The production method of theoptical disk media, evaluation method, and presentation rule of Table 3are the same as those of the above described Example 1. The composition,51% Ag and 49% Te in mass percent, is equal to 55% Ag and 45% Te inatomic percent. TABLE 3 Recording layer Re- Reproducing Exam- Finecording 8T light ple Layer crystal power C/N resistance No. structuregrains Matrix (mW) (dB) (dB) 13 Substrate Ag₅₁Te₄₉ SiO₂ 9.5 56.2 0 14Substrate Ag₅₁Te₄₉ Al₂O₃ 9.9 56.2 0 15 Substrate Ag₅₁Te₄₉ Ta₂O₅ 9.1 56.40 16 Substrate Ag₅₁Te₄₉ SiN 9.6 55.8 0 17 Substrate Ag₅₁Te₄₉ AlN 9.755.3 0 18 Substrate Ag₅₁Te₄₉ TaN 9.7 55.9 0 19 Cover Ag₅₁Te₄₉ SiO₂ 5.255.9 0 20 Cover Ag₅₁Te₄₉ Al₂O₃ 5.8 56.1 0 21 Cover Ag₅₁Te₄₉ Ta₂O₅ 5.755.7 0 22 Cover Ag₅₁Te₄₉ SiN 5.3 55.1 0 23 Cover Ag₅₁Te₄₉ AlN 5.5 55.7 024 Cover Ag₅₁Te₄₉ TaN 5.2 55.2 0

In the optical disk media of No. 16 and No. 22 shown in Table 3, theparticle diameter of the fine crystal grains of the recording layer wasabout 3 to 7 nm in the non-recorded portions, and 30 to 80 nm in therecorded portions. This indicates that laser irradiation has increasedthe particle diameter of the fine crystal grains.

As shown in Table 3, the optical information recording media with arecording layer that is formed by co-sputtering from the fine crystalgrains of Ag₅₁Te₄₉ (mass %) alloy and the matrix of an oxide dielectricor a nitride dielectric exhibited a high reproducing C/N ratio and goodreproducing light resistance. Also, the optical disk media with arecording layer formed from the fine crystal grains of Ag₆₁Te₃₉ (mass %)or Ag₄₆Te₅₄ (mass %) alloy and the matrix of an oxide dielectric or anitride dielectric shown in Table 3 exhibited the same results as thereproducing characteristics shown in Table 3.

EXAMPLE 3

Optical disk media having fine crystal grains formed of Cu—In alloy wereproduced with the same method as Example 1 described above, and theircharacteristics were evaluated. The optical disk media had two layerstructures, one being the substrate-side incident type medium as withthe above described first embodiment and the other being the coverlayer-side incident type medium as with the above described secondembodiment. Table 4 shows the compositions of the fine crystal grainsand matrix of the recording layer, recording power, reproducing signalquality (C/N ratio of 8T signal), and reproducing light resistance(difference in the C/N ratio of 8T signal). The production method of theoptical disk media, evaluation method, and presentation rule of Table 4are the same as those of the above described Example 1. TABLE 4Recording layer Re- Reproducing Exam- Fine cording 8T light ple Layercrystal power C/N resistance No. structure grains Matrix (mW) (dB) (dB)25 Substrate Cu₅₀In₅₀ SiO₂ 9.3 56.4 0 26 Substrate Cu₅₀In₅₀ Al₂O₃ 9.355.9 0 27 Substrate Cu₅₀In₅₀ Ta₂O₅ 9.6 55.6 0 28 Substrate Cu₅₀In₅₀ SiN9.7 56.2 0 29 Substrate Cu₅₀In₅₀ AlN 9.1 55.8 0 30 Substrate Cu₅₀In₅₀TaN 9.5 55.2 0 31 Cover Cu₅₀In₅₀ SiO₂ 5.3 56.4 0 32 Cover Cu₅₀In₅₀ Al₂O₃5.1 56.1 0 33 Cover Cu₅₀In₅₀ Ta₂O₅ 5.7 55.2 0 34 Cover Cu₅₀In₅₀ SiN 5.555.7 0 35 Cover Cu₅₀In₅₀ AlN 5.4 55.8 0 36 Cover Cu₅₀In₅₀ TaN 5.7 55.1 0

In the optical disk media of No. 26 and No. 32 shown in Table 4, theparticle diameter of the fine crystal grains of the recording layer wasabout 3 to 7 nm in the non-recorded portions, and 30 to 80 nm in therecorded portions. This indicates that laser irradiation has increasedthe particle diameter of the fine crystal grains.

As shown in Table 4, the optical information recording media with arecording layer that is formed by co-sputtering from the fine crystalgrains of Cu₅₀In₅₀ (mass %) alloy and the matrix of an oxide dielectricor a nitride dielectric exhibited a high reproducing C/N ratio and goodreproducing light resistance. Also, the optical disk media with arecording layer formed from the fine crystal grains of Cu₆₀In₄₀ (mass %)or Cu₅In₉₅ (mass %) alloy and the matrix of an oxide dielectric or anitride dielectric shown in Table 3 exhibited the same results as thereproducing characteristics shown in Table 4.

The recording laser beam and the reproducing laser beam used in theabove described Examples 1 to 3 had a wavelength of 405 nm, but it wasconfirmed that the same effects and results are achieved if the laserbeam has a wavelength in a range of 380 to 430 nm. In the abovedescribed Examples 1 to 3, when the laser beam had a wavelength of lessthan 380 nm, the laser light absorption in the PC substrate increaseddrastically, resulting in unfavorable recording performance orreproducing performance. On the other hand, when the laser beam had awavelength of 440 nm or more, the absorption rate in the recording layerstarted to decrease, because of which a higher recording power wasnecessary at the time of recording, and high-speed recording ofinformation became difficult. Accordingly, the laser beam used for therecording and reproduction of information should preferably have awavelength in a range of 380 to 430 nm.

EXAMPLE 4

Next, the influence of linear speed on the reproducing characteristicswas investigated. FIG. 5 is a graph showing the influence of linearspeed on the quality of reproducing signal, the horizontal axisrepresenting the linear speed of the optical disk medium duringrecording and reproduction and the vertical axis representing the C/Nratio of 8T signal. In this fourth example, a substrate-side incidenttype medium shown in the above described first embodiment was used asthe optical disk medium, its recording layer being formed byco-sputtering, with the matrix made of SiO₂ and the fine crystal grainsmade of one of an Ag₉₈Pd₁Cu₁ alloy, Ag₅₁Te₄₉ alloy, and Cu₅₀In₅₀ alloy.With this optical disk medium, the linear speed was changed in the rangeof from 3.0 to 11.0 m/sec, while a signal with a period of 8T wasrecorded and reproduced, and the C/N ratio for each linear speed wasmeasured. The production method of the optical disk media andmeasurement method other than the above are the same as those of theabove described Example 1. The measurement results are shown in FIG. 5.As shown in FIG. 5, the above optical recording medium exhibited goodC/N ratio values in the above linear speed range, which indicates thatit is applicable to high-speed recording.

Also, the optical disk media with a recording layer formed byco-sputtering using the alloys with the compositions shown in the firstto third examples for the fine crystal grains and the above mentioneddielectrics exhibited the same results as those shown in FIG. 5.

While, in the above first to fourth examples, as described above, therecording layer was formed by co-sputtering using an alloy target and adielectric target, these alloy and dielectrics may be sintered or fusedtogether into one target, and the recording layer may be formed bysputtering using this target. In this case, too, the results were thesame as those shown in FIG. 5.

EXAMPLE 5

Next, the reproducing characteristics of optical disk media having adouble-layer recording layer were evaluated. The optical disk media hadtwo layer structures, one being the substrate-side incident type mediumas with the above described third embodiment and the other being thecover layer-side incident type medium as with the above described fourthembodiment. That is, the layer structure of the substrate-side incidenttype medium was PC substrate/dielectric layer/first recordinglayer/dielectric layer/optical separation layer/dielectric layer/secondrecording layer/dielectric layer/reflective layer/UV adhesivelayer/dummy PC substrate. The layer structure of the cover layer-sideincident type medium was PC substrate/reflective layer/dielectriclayer/second recording layer/dielectric layer/optical separationlayer/dielectric layer/first recording layer/dielectric layer/UVadhesive layer/PC cover layer. The fine crystal grains of the recordinglayer were made of one of an Ag₉₈Pd₁Cu₁ alloy, Ag₅₁Te₄₉ alloy, andCu₅₀In₅₀ alloy, and the matrix was made of SiO₂. The first recordinglayer had a thickness of 7 nm, and the second recording layer 12 nm. Thestructure and production method of these optical disk media other thanthe above are the same as the above described Example 1.

The reproducing characteristics of the optical disk media thus producedwere evaluated. The evaluation method was the same as that of the abovedescribed Example 1. Table 5 shows the reproducing characteristics ofthe first recording layer, i.e., compositions of the fine crystal grainsand matrix of the first recording layer, recording power, reproducingsignal quality (C/N ratio of 8T signal), and reproducing lightresistance (difference in the C/N ratio of 8T signal). Table 6 shows thereproducing characteristics of the second recording layer, i.e.,compositions of the fine crystal grains and matrix of the secondrecording layer, recording power, reproducing signal quality (C/N ratioof 8T signal), and reproducing light resistance (difference in the C/Nratio of ST signal). TABLE 5 Re- Recording layer Re- producing Exam-Fine cording 8T light ple Layer crystal power C/N resistance No.structure grains Matrix (mW) (dB) (dB) 37 Substrate Ag₉₈Pd₁Cu₁ SiO₂ 9.156.1 0 38 Substrate Ag₅₁Te₄₉ SiO₂ 10.2 55.7 0 39 Substrate Cu₅₀In₅₀ SiO₂9.4 56.0 0 40 Cover Ag₉₈Pd₁Cu₁ SiO₂ 5.3 55.6 0 41 Cover Ag₅₁Te₄₉ SiO₂5.5 56.2 0 42 Cover Cu₅₀In₅₀ SiO₂ 5.9 55.3 0

TABLE 6 Re- Recording layer Re- producing Exam- Fine cording 8T lightple Layer crystal power C/N resistance No. structure grains Matrix (mW)(dB) (dB) 43 Substrate Ag₉₈Pd₁Cu₁ SiO₂ 9.9 55.6 0 44 Substrate Ag₅₁Te₄₉SiO₂ 10.7 55.8 0 45 Substrate Cu₅₀In₅₀ SiO₂ 10.2 55.4 0 46 CoverAg₉₈Pd₁Cu₁ SiO₂ 5.8 55.1 0 47 Cover Ag₅₁Te₄₉ SiO₂ 6.1 55.7 0 48 CoverCu₅₀In₅₀ SiO₂ 6.3 55.1 0

Table 5 and Table 6 indicate that, in the double-layer recording mediahaving a recording layer separated by an optical separation layer, thereproducing C/N ratio of the first and second recording layers isequally high as that of the recording media having a single-layerrecording layer, and that the reproducing light resistance issatisfactorily acceptable for actual use.

INDUSTRIAL APPLICABILITY

The present invention is suitably applicable to optical informationrecording media such as CD-R, DVD-R, and the like, which usesirradiation of a blue-violet semiconductor laser beam to record andreproduce information.

1. An optical information recording medium including a substrate and arecording layer formed on the substrate, information being recorded andreproduced by irradiating light to this recording layer, characterizedin that the recording layer includes a matrix made of a dielectric and aplurality of fine crystal grains made of a metal or an alloy anddispersed in the matrix, and, by irradiating light to the recordinglayer, a size of the fine crystal grains is changed in a portionirradiated by the light, whereby information is recorded.
 2. The opticalinformation recording medium according to claim 1, characterized in thatthe fine crystal grains are made of a metal or an alloy of two or moremetals selected from the group consisting of Ag, Cu, In, Pd, and Te. 3.The optical information recording medium according to claim 2,characterized in that the fine crystal grains are made of an Ag—Pd—Cualloy containing 0.3 to 25 mass % of Pd and 0.3 to 25 mass % of Cu, thebalance being Ag and unavoidable impurities.
 4. The optical informationrecording medium according to claim 2, characterized in that the finecrystal grains are made of an Ag—Te alloy containing 38 to 55 mass % ofTe, the balance being Ag and unavoidable impurities.
 5. The opticalinformation recording medium according to claim 2, characterized in thatthe fine crystal grains are made of a Cu—In alloy containing 40 to 95mass % of In, the balance being Cu and unavoidable impurities.
 6. Theoptical information recording medium according to claim 1, characterizedin that the dielectric is an oxide dielectric.
 7. The opticalinformation recording medium according to claim 6, characterized in thatthe oxide dielectric is one or two or more oxides selected from thegroup consisting of silicon oxide, aluminum oxide, and tantalum oxide.8. The optical information recording medium according to claim 1,characterized in that the dielectric is a nitride dielectric.
 9. Theoptical information recording medium according to claim 8, characterizedin that the nitride dielectric is one or two or more nitrides selectedfrom the group consisting of silicon nitride, aluminum nitride, andtantalum nitride.
 10. The optical information recording medium accordingto claim 1 characterized by including a first dielectric layer formedbetween the substrate and the recording layer, a second dielectric layerformed on the recording layer, and a reflective layer formed on thesecond dielectric layer, the substrate being a transparent substrate,wherein the light is made incident toward the recording layer from theside of the substrate.
 11. The optical information recording mediumaccording to claim 1, characterized by including a reflective layerformed between the substrate and the recording layer, a first dielectriclayer formed between the reflective layer and the recording layer, asecond dielectric layer formed on the recording layer, and a lighttransmission layer formed on the second dielectric layer, wherein thelight is made incident toward the recording layer from the side of thelight transmission layer.
 12. The optical information recording mediumaccording to claim 1, characterized in that the recording layer consistsof a plurality of layers, which are separated from each other by aninterlayer optical separation layer.
 13. The optical informationrecording medium according to claim 1, characterized in that the lightis a laser beam with a wavelength of 380 to 430 nm.
 14. An opticalinformation recording/reproducing apparatus characterized in that lightis irradiated to the optical information recording medium according toclaim 1 to change the size of the fine crystal grains. In thelight-irradiated portion of the recording layer so as to change thereflectance in the portion to record information, and the information isreproduced by detecting a difference in the reflectance of the recordinglayer.